This is a multicenter randomized controlled clinical trial with a superiority design. At approximately 4 months after the end of curative intent treatment patients will be randomized 1:1 to either the intervention (18F FDG PET/CT) or the control group (usual care, CT-based follow-up). Randomization will be done stratifying for histology and treatment.

• The intervention group (n = 345) consists of usual care until 3 years of follow-up (see comparator) with additional whole-body 18F FDG PET/CT scans (from the skull to, at least, the midfemoral region) during follow-up visits at 6 months, 12 months, 18 months, 24 months, and 36 months of follow-up. After the 36-month follow-up period, patients will receive follow-up usual care (i.e. CT-scans).
• The control group (n = 345) consists of regular follow-up visits with physical check-ups and CT-scans at least every 6 months for the first 2 years and then at least yearly CT-scans until 3 years of follow-up. In case of suspected recurrence/metastasis or inconclusive results of a CT-scan (eg, after radiotherapy), 18F FDG PET/CT should be considered.

• Overall survival
• Recurrences
• Event-free survival

• Cytological or histologically proven stage III non-small cell lung cancer before start of curative intent treatment
• Treated with curative intent and started follow-up care
• All adjuvant treatments are permitted as co-intervention during follow-up care
• Age 18 years or older
• ECOG Performance Status classification 0-2 at moment of inclusion
• Written and signed informed consent by the patient or their representative (with the understanding that consent may be withdrawn by the patient or their representative at any time without consequences to future medical care)

• Life expectancy shorter than 6 months at the end of curative intent treatment
• Evidence of recurrence after end of curative intent treatment and before randomization (4 months follow-up)
• Any condition that, in the opinion of the investigator, would interfere with evaluation of the intervention or interpretation of HRQOL or other study results.